urllib – simple interface for network resource access

Purpose:Accessing remote resources that don’t need authentication, cookies, etc.
Available In:1.4 and later

The urllib module provides a simple interface for network resource access. Although urllib can be used with gopher and ftp, these examples all use http.

HTTP GET

Note

The test server for these examples is in BaseHTTPServer_GET.py, from the PyMOTW examples for BaseHTTPServer. Start the server in one terminal window, then run these examples in another.

An HTTP GET operation is the simplest use of urllib. Simply pass the URL to urlopen() to get a “file-like” handle to the remote data.

import urllib

response = urllib.urlopen('http://localhost:8080/')
print 'RESPONSE:', response
print 'URL     :', response.geturl()

headers = response.info()
print 'DATE    :', headers['date']
print 'HEADERS :'
print '---------'
print headers

data = response.read()
print 'LENGTH  :', len(data)
print 'DATA    :'
print '---------'
print data

The example server takes the incoming values and formats a plain text response to send back. The return value from urlopen() gives access to the headers from the HTTP server through the info() method, and the data for the remote resource via methods like read() and readlines().

$ python urllib_urlopen.py
RESPONSE: <addinfourl at 10180248 whose fp = <socket._fileobject object at 0x935c30>>
URL     : http://localhost:8080/
DATE    : Sun, 30 Mar 2008 16:27:10 GMT
HEADERS :
---------
Server: BaseHTTP/0.3 Python/2.5.1
Date: Sun, 30 Mar 2008 16:27:10 GMT

LENGTH  : 221
DATA    :
---------
CLIENT VALUES:
client_address=('127.0.0.1', 54354) (localhost)
command=GET
path=/
real path=/
query=
request_version=HTTP/1.0

SERVER VALUES:
server_version=BaseHTTP/0.3
sys_version=Python/2.5.1
protocol_version=HTTP/1.0

The file-like object is also iterable:

import urllib

response = urllib.urlopen('http://localhost:8080/')
for line in response:
    print line.rstrip()

Since the lines are returned with newlines and carriage returns intact, this example strips them before printing the output.

$ python urllib_urlopen_iterator.py
CLIENT VALUES:
client_address=('127.0.0.1', 54380) (localhost)
command=GET
path=/
real path=/
query=
request_version=HTTP/1.0

SERVER VALUES:
server_version=BaseHTTP/0.3
sys_version=Python/2.5.1
protocol_version=HTTP/1.0

Encoding Arguments

Arguments can be passed to the server by encoding them and appending them to the URL.

import urllib

query_args = { 'q':'query string', 'foo':'bar' }
encoded_args = urllib.urlencode(query_args)
print 'Encoded:', encoded_args

url = 'http://localhost:8080/?' + encoded_args
print urllib.urlopen(url).read()

Notice that the query, in the list of client values, contains the encoded query arguments.

$ python urllib_urlencode.py
Encoded: q=query+string&foo=bar
CLIENT VALUES:
client_address=('127.0.0.1', 54415) (localhost)
command=GET
path=/?q=query+string&foo=bar
real path=/
query=q=query+string&foo=bar
request_version=HTTP/1.0

SERVER VALUES:
server_version=BaseHTTP/0.3
sys_version=Python/2.5.1
protocol_version=HTTP/1.0

To pass a sequence of values using separate occurrences of the variable in the query string, set doseq to True when calling urlencode().

import urllib

query_args = { 'foo':['foo1', 'foo2'] }
print 'Single  :', urllib.urlencode(query_args)
print 'Sequence:', urllib.urlencode(query_args, doseq=True  )
$ python urllib_urlencode_doseq.py
Single  : foo=%5B%27foo1%27%2C+%27foo2%27%5D
Sequence: foo=foo1&foo=foo2

To decode the query string, see the FieldStorage class from the cgi module.

Special characters within the query arguments that might cause parse problems with the URL on the server side are “quoted” when passed to urlencode(). To quote them locally to make safe versions of the strings, you can use the quote() or quote_plus() functions directly.

import urllib

url = 'http://localhost:8080/~dhellmann/'
print 'urlencode() :', urllib.urlencode({'url':url})
print 'quote()     :', urllib.quote(url)
print 'quote_plus():', urllib.quote_plus(url)

Notice that quote_plus() is more aggressive about the characters it replaces.

$ python urllib_quote.py

urlencode() : url=http%3A%2F%2Flocalhost%3A8080%2F%7Edhellmann%2F
quote()     : http%3A//localhost%3A8080/%7Edhellmann/
quote_plus(): http%3A%2F%2Flocalhost%3A8080%2F%7Edhellmann%2F

To reverse the quote operations, use unquote() or unquote_plus(), as appropriate.

import urllib

print urllib.unquote('http%3A//localhost%3A8080/%7Edhellmann/')
print urllib.unquote_plus('http%3A%2F%2Flocalhost%3A8080%2F%7Edhellmann%2F')
$ python urllib_unquote.py

http://localhost:8080/~dhellmann/
http://localhost:8080/~dhellmann/

HTTP POST

Note

The test server for these examples is in BaseHTTPServer_POST.py, from the PyMOTW examples for the BaseHTTPServer. Start the server in one terminal window, then run these examples in another.

To POST data to the remote server, instead of using GET, pass the encoded query arguments as data to urlopen() instead of appending them to the URL.

import urllib

query_args = { 'q':'query string', 'foo':'bar' }
encoded_args = urllib.urlencode(query_args)
url = 'http://localhost:8080/'
print urllib.urlopen(url, encoded_args).read()
$ python urllib_urlopen_post.py
Client: ('127.0.0.1', 54545)
Path: /
Form data:
    q=query string
    foo=bar

You can send any byte-string as data, in case the server expects something other than url-encoded form arguments in the posted data.

Paths vs. URLs

Some operating systems use different values for separating the components of paths in local files than URLs. To make your code portable, you should use the functions pathname2url() and url2pathname() to convert back and forth. Since I am working on a Mac, I have to explicitly import the Windows versions of the functions. Using the versions of the functions exported by urllib gives you the correct defaults for your platform, so you do not need to do this.

import os

from urllib import pathname2url, url2pathname

print '== Default =='
path = '/a/b/c'
print 'Original:', path
print 'URL     :', pathname2url(path)
print 'Path    :', url2pathname('/d/e/f')
print

from nturl2path import pathname2url, url2pathname

print '== Windows, without drive letter =='
path = path.replace('/', '\\')
print 'Original:', path
print 'URL     :', pathname2url(path)
print 'Path    :', url2pathname('/d/e/f')
print

print '== Windows, with drive letter =='
path = 'C:\\' + path.replace('/', '\\')
print 'Original:', path
print 'URL     :', pathname2url(path)
print 'Path    :', url2pathname('/d/e/f')

There are two Windows examples, with and without the drive letter at the prefix of the path.

$ python urllib_pathnames.py

== Default ==
Original: /a/b/c
URL     : /a/b/c
Path    : /d/e/f

== Windows, without drive letter ==
Original: \a\b\c
URL     : /a/b/c
Path    : \d\e\f

== Windows, with drive letter ==
Original: C:\\a\b\c
URL     : ///C:/a/b/c
Path    : \d\e\f

Simple Retrieval with Cache

Retrieving data is a common operation, and urllib includes the urlretrieve() function so you don’t have to write your own. urlretrieve() takes arguments for the URL, a temporary file to hold the data, a function to report on download progress, and data to pass if the URL refers to a form where data should be POSTed. If no filename is given, urlretrieve() creates a temporary file. You can delete the file yourself, or treat the file as a cache and use urlcleanup() to remove it.

This example uses GET to retrieve some data from a web server:

import urllib
import os

def reporthook(blocks_read, block_size, total_size):
    if not blocks_read:
        print 'Connection opened'
        return
    if total_size < 0:
        # Unknown size
        print 'Read %d blocks' % blocks_read
    else:
        amount_read = blocks_read * block_size
        print 'Read %d blocks, or %d/%d' % (blocks_read, amount_read, total_size)
    return

try:
    filename, msg = urllib.urlretrieve('http://blog.doughellmann.com/', reporthook=reporthook)
    print
    print 'File:', filename
    print 'Headers:'
    print msg
    print 'File exists before cleanup:', os.path.exists(filename)

finally:
    urllib.urlcleanup()

    print 'File still exists:', os.path.exists(filename)

Since the server does not return a Content-length header, urlretrieve() does not know how big the data should be, and passes -1 as the total_size argument to reporthook().

$ python urllib_urlretrieve.py
Connection opened
Read 1 blocks
Read 2 blocks
Read 3 blocks
Read 4 blocks
Read 5 blocks
Read 6 blocks
Read 7 blocks
Read 8 blocks
Read 9 blocks
Read 10 blocks
Read 11 blocks
Read 12 blocks
Read 13 blocks
Read 14 blocks
Read 15 blocks
Read 16 blocks
Read 17 blocks
Read 18 blocks
Read 19 blocks

File: /var/folders/9R/9R1t+tR02Raxzk+F71Q50U+++Uw/-Tmp-/tmp3HRpZP
Headers:
Content-Type: text/html; charset=UTF-8
Last-Modified: Tue, 25 Mar 2008 23:09:10 GMT
Cache-Control: max-age=0 private
ETag: "904b02e0-c7ff-47f6-9f35-cc6de5d2a2e5"
Server: GFE/1.3
Date: Sun, 30 Mar 2008 17:36:48 GMT
Connection: Close

File exists before cleanup: True
File still exists: False

URLopener

urllib provides a URLopener base class, and FancyURLopener with default handling for the supported protocols. If you find yourself needing to change their behavior, you are probably better off looking at the urllib2 module, added in Python 2.1.

See also

urllib
Standard library documentation for this module.
urllib2
Updated API for working with URL-based services.
urlparse
Parse URL values to access their components.
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